Have you ever stopped to think about all the things that happen when you execute a simple .NET program? This talk will delve into the internals of the recently open-sourced .NET Core runtime, looking at what happens, when it happens and why. Making use of freely available tools such as 'PerfView', we'll examine the Execution Engine, Type Loader, Just-in-Time (JIT) Compiler and the CLR Hosting API to see how all these components play a part in making 'Hello World' possible.

1. Organized by Donating to
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Runtime Internals
by Matt Warren
NYAN conference

2. From ‘dotnet run’
to “Hello World”
@matthewwarren
mattwarren.org

3. www.contrastsecurity.com/contrast-community-edition

4. I ♥️‘.NET Internals’

5. Understand one level below
your usual abstraction
Neal Ford

6. Demo – “Hello World”

7. Outline
• Main Components
• Hosting the runtime
• CLR Initialisation
• Type Loader
• JIT Compilation
• Everything Else

8. Main Components

9. CoreCLR Repository
• 1.6 million LOC under src
• 7.6 million LOC under tests
• 22,744 Files (6,668 source & 16,076 test)
– 7,290 C# (1,529 source & 5,761 test)
– 3,641 C and C++
– 3,799 IL (tests)
– 139 Assembly, 10 Python & 6 Perl!!

18. Virtual Machine (VM)
• Type System, Generics
• Built-in Types
• Loading types/classes
• Threading
• Exception Handling and Stack Walking
• Event Tracing and Profiling
• P/Invoke

19. Hosting

20. Hosting API
1. Identify the managed entry point
2. Find and load CoreCLR.dll
3. Get an ICLRRuntimeHost2 Instance
4. Set start-up flags and start the runtime
5. Preparing AppDomain settings
6. Create the AppDomain
7. Run managed code
8. Clean up
https://docs.microsoft.com/en-us/dotnet/core/tutorials/netcore-hosting

21. Demo – Hosting API

22. Initialisation

23. Initialising the CLR
• Phase 1 - Set-up infrastructure for all components
• Phase 2 - Initialise the core, low-level components
• Phase 3 - Start-up the low-level components, i.e. error
handling, profiling API, debugging
• Phase 4 - Start the main components, i.e. GC & AppDomains
• Phase 5 - Final setup and send out a notification
http://mattwarren.org/2017/02/07/The-68-things-the-CLR-does-before-
executing-a-single-line-of-your-code/

24. Demo - PerfView

25. ImageCourtesyof
JuliaEvans
@b0rk–jvns.ca

29. https://docs.microsoft.com/en-us/dotnet/standard/garbage-collection/fundamentals

30. Type Loader

33. http://mattwarren.org/2017/06/15/How-the-.NET-Rutime-loads-a-Type/

34. JIT Compilation

35. http://mattwarren.org/2017/12/15/How-does-.NET-JIT-a-
method-and-Tiered-Compilation/
Before JIT-ing

36. http://mattwarren.org/2017/12/15/How-does-.NET-JIT-a-
method-and-Tiered-Compilation/
Before JIT-ing
After JIT-ing

37. http://mattwarren.org/2017/12/15/How-does-.NET-JIT-a-
method-and-Tiered-Compilation/
Before JIT-ing
After JIT-ing with ‘Tiered Compilation’

38. http://mattwarren.org/2017/12/15/How-does-.NET-JIT-a-
method-and-Tiered-Compilation/
After JIT-ing with ‘Tiered Compilation’ - Optimised

39. Everything Else

40. Marshalling and P/Invoke

41. Resources
• http://mattwarren.org/tags/#Internals
– Resources for Learning about .NET Internals
– Exploring the Internals of the .NET Runtime
– Tools for Exploring .NET Internals
– Presentations and Talks covering '.NET Internals'
• Book of the Runtime (BotR)
– https://github.com/dotnet/coreclr/tree/master/Document
ation/botr